1. Field of the Invention
The present invention generally relates to a touch panel, and more particularly to a driving signal generating system for providing a driving signal to a touch panel.
2. Description of the Related Art
A touch panel may be combined with a display screen to result in a touch screen. Touch screens have been widely used as input interfaces for electronic devices for detecting touch inputs within a display area. The touch technology utilized in the touch panel may be, for example, capacitive, resistive or optical, among which capacitive touch technology is presently the most popular.
A capacitive touch panel is typically made of horizontal electrodes and vertical electrodes, cross points of which are defined as touch points. When the touch panel is operated, an electric field is formed between two electrodes at the touch point. A finger touching the panel blocks some of the electric field, therefore reducing capacitance at the touch point. A touch point may thus be detected according to change of the capacitance.
In a conventional touch system, a driving signal is used to drive horizontal electrodes, and an induced signal is generated at vertical electrodes due to capacitive coupling effect. The induced signal is then processed by a signal processing technique. When a finger or a conductive object (e.g., a stylus) touches a driven horizontal electrode, the electric field associated with the touch point is affected to generate an abnormal induced signal at a corresponding vertical electrode.
FIG. 1A schematically shows a conventional driving signal generating system for generating a square wave driving signal for a touch panel. A level shifter 11 receives a square wave signal and pulls up a level of the square wave signal to generate a square wave driving signal. A charge pump 12 is commonly used to provide a power to the level shifter 11 to increase a level of the square wave driving signal in order to resist noise. FIG. 1B shows an exemplary square wave signal 111 and a generated square wave driving signal 112. The power provided by the charge pump 12, however, may be affected by temperature such that the level of the square wave driving signal 112 may accordingly be changed to that of a square wave driving signal 113 as exemplified in FIG. 1B, thereby reducing detection accuracy. In order to make to the power provided by the charge pump 12 less liable to temperature, a low-dropout (LDO) regulator may be adopted but at a cost of increasing circuit area.
A need has thus arisen to propose a novel driving signal generating system for providing a stable driving signal for a touch panel, without being affected by temperature and increasing circuit area, to increase detection accuracy at a touch point.